I have experienced some cloudy result even after careful cleaning. My glass instructor told me that, with a small, top element kiln like mine, sometimes there is not enough ventilation. Any fumes put off by glue, kiln paper, and anything else is trapped in the kiln, rises to the top, burns and falls in a haze onto the glass. I sand blasted the pieces that were affected and I am getting ready to fire them again. If you don’t have access to a sand blaster you can also polish them off with some very fine grit automotive wet/dry sand paper. I found some at Walmart. ‘Hope this helps!